If you want a pretty comprehensive comparison of nearly all of the available internal hubs go here: Internal-Gear Hubs You can compare gear ranges and even see how closely spaced the gears are on a particular hub.

I've used the SRAM dual-drive 3X8 and a Schlumpf Mountain Drive on a trike. The MD was nearly indestructible with only one minor repair in 27,000 miles while the SRAM dual-drive was much less robust. It originally came with the highly praised SACHS Spectro 7 3X8 and when that failed switched to SRAM DD which failed twice in the remaining mileage. One really big problem is finding someone who will fix one of these hubs. No bike shop in my town would fix the Spectro 7 and the cost of having it only partially rebuilt by the one rebuilder I was able to contact was nearly equal to buying a brand new DD. If it had been a complete rebuild with many new components it would have been worth it but the partial rebuild was only replacing the bearings. Things like pawls and springs which also wear would not be replaced. I tossed the wheel and bought a complete new rear wheel.